1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus such as a copier, a facsimile machine, or a printer that performs image formation by transferring a toner image formed on a surface of an image bearing member onto a recording medium, and a control method for controlling the image forming apparatus.
2. Description of the Background
Related-art image forming apparatuses, such as a copier, a facsimile machine, a printer, or a multifunction printer having two or more of copying, printing, scanning, and facsimile functions, form a toner image on a recording medium (e.g., a sheet) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image bearing member (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
Such image forming apparatuses generally determine whether or not a request for subsequent image formation is present at a predetermined determination time (hereinafter referred to as shutdown determination time) after completion of a current image formation operation. When determining that the request for subsequent image formation is not present, the image forming apparatuses shut down predetermined operations performed therein in order to prevent abrasion of components and deterioration of toner. Generally, the image forming apparatuses shut down such operations as rotation of the image bearing member and application of a charging bias from the charger and a developing bias from the developing device in accordance with a predetermined shutdown procedure. By contrast, when receiving the request for subsequent image formation, the image forming apparatuses start up the operations thus shut down so that subsequent image formation is started in accordance with the request.
As is obvious, it requires time to shut down or start up the operations. Further, new image formation cannot be started while the operations are shut down or started up. Consequently, in a case in which the request for subsequent image formation is received after the process to shut down the operations is started, the start of subsequent image formation is delayed compared with a case in which the request is received before the process to shut down the operations is started.
Published Unexamined Japanese Patent Application No. (hereinafter referred to as JP-A-) 2007-069357 discloses an image forming apparatus that estimates a time required to process print data during continuous image formation so that output of an image of the first page to a printer engine is delayed depending on the time thus estimated. When image data with a larger processing load is included in continuous image formation, output of a request for forming images based on such image data is delayed. Consequently, the request may not be output before the shutdown determination time after previous image formation is completed. As a result, the printer engine is shut down even during continuous image formation, and start of subsequent image formation based on such image data is delayed for at least the time required to shut down the operations and then restart such operations.
According to the image forming apparatus disclosed in JP-A-2007-069357, even when the image data with a larger processing load is included in continuous image formation, output of the image of the first page to the printer engine is delayed only for a time corresponding to the time required to process the image data. Accordingly, the printer engine is prevented from being shut down during continuous image formation. As a result, downtime caused by shutdown of the printer engine during continuous image formation can be reduced.
When determining that the request for subsequent image formation is not present at the shutdown determination time, related-art image forming apparatuses such as the image forming apparatus disclosed in JP-A-2007-069357 enter the shutdown sequence to shut down the predetermined operations. The shutdown sequence is not suspended, but continued until completed even when the request for subsequent image formation is received during the shutdown sequence. Consequently, in a case in which the request for subsequent image formation is received during the shutdown sequence, start of subsequent image formation in accordance with the request is delayed for the time required to perform the rest of the shutdown sequence and then the startup sequence performed after completion of the shutdown sequence.